The present invention relates to a printing apparatus.
As well known in the art, some of printing apparatuses perform color printing with using color toners supplied from toner cartridges. In many of printing apparatuses of this kind, the amounts of residual toners (hereinafter, referred to as residual toner amounts) in color toner cartridges are displayed in a display of a control panel to inform the operator of a timing when the color reproducibility of a color image is deteriorated or that when a toner cartridge is to be replaced.
FIG. 9 shows an example of a control panel 30 which displays residual toner amounts of toner cartridges in a display 31 disposed together with plural buttons on the upper face of the control panel 30. In the vicinity of the right side of the lower edge of the display 31, four oval indicators 32 colored respectively by CMYK (cyan, magenta, yellow and black) colors are arrayed. In the display 31 and above the four indicators 32, bar graphs respectively showing residual amounts of toners of colors indicated by the indicators are displayed. From the indicators 32 and the bar graphs, the operator can immediately recognize the residual toner amounts of the respective colors.
Some of printing apparatuses are configured so that color printing and monochrome printing are switched over in accordance with the combination of colors of toners of toner cartridges which are set in the apparatus. When four toner cartridges respectively filled with CMYK toners are set, for example, a printing apparatus of this kind operates in a color printing mode, and, when four toner cartridges filled with toners of K are set, operates in a monochrome printing mode.
When the above-mentioned method of displaying residual toner amounts is applied to a printing apparatus of this kind, in the monochrome printing mode, residual toner amounts of four toner cartridges for K are displayed respectively in the form of the bar graphs in the display 31 of the control panel 30. In this case, the colors of the toners the residual amounts of which are actually indicated by the bar graphs do not coincide with the colors of the indicators 32, whereby the operator is confused.
In order to provide the user with a message indicating that the toner cartridge is to be replaced with a new one, there is installed a residual toner amount detector which detects that there is no amount of residual toner in a toner cartridge.
Recently, in order to reduce the production cost of a printing apparatus of such a kind, there is adopted a configuration where a residual toner amount detector which is not highly accurate is installed, or that where a residual toner amount detector is not installed. Instead, an amount of consumed toner is calculated by counting the number of actually printed dots.
In both the configurations where a residual toner amount detector which is not highly accurate is installed, and where a residual toner amount detector is not installed, however, the accuracy of detecting the residual toner amount is not so high. Consequently, there is a problem in that a message indicating that the toner cartridge is to be replaced with a new one would be displayed although a considerable amount of toner remains in the toner cartridge.
It is well-known a printing apparatus in which a toner cartridge for supplying toner to a photosensitive drum is sequentially changed one by one every time when printing is performed on a unit number of sheets.
When a residual toner amount detector is not installed on such a printing apparatus, the printing apparatus cannot judge whether toner remains in a cartridge or not. In a case where a toner cartridge is sequentially changed one by one every time when printing is performed on a unit number of sheets, there is a problem in that a situation may occur where printing must be performed with using a toner cartridge in which toner is consumed up.